A 15-year-old accused of fatally shooting his older sister at their family's rural Arkansas home stood before a judge by himself Tuesday and was ordered held on $750,000 bond, a prosecutor said.

Prosecutor David Gibbons said he plans to charge the boy with first-degree murder as an adult by the end of next week "because of the nature of the crime." The boy hasn't been identified because of his age and his court hearing was closed to the public. The judge even forced his aunt and uncle out of the courtroom, leaving the boy to stand alone before the judge, Gibbons said.

The prosecutor said Circuit Judge Bill Pearson ordered that the boy be assigned a public defender. The public defender in Franklin County, where the boy lives with his family, didn't immediately return a phone message seeking comment. The boy's next court date is March 1.

Franklin County Sheriff Anthony Boen said the boy showed up at the sheriff's office Sunday morning and told investigators he had shot and killed his 16-year-old sister at their home near Ozark, a town of about 3,600 roughly 120 miles northwest of Little Rock. Boen said Tuesday that authorities were still awaiting preliminary autopsy results.

Boen said the boy appeared remorseful and had tears in his eyes when he turned himself in.

"He just said that he had just shot and killed his sister," Boen said. "... He didn't give a motive."

The teen likely killed his sister sometime after 8 a.m. Sunday, when his parents left to go grocery shopping in Fort Smith, about 40 miles away, Boen said. The boy turned himself in at the sheriff's department about 9:30 a.m.

Investigators confiscated multiple guns from the family's home and vehicle, and were trying to determine which weapon had been used. The sheriff said the boy and his father were avid hunters.

The hearing was held in Russellville, about 50 miles from the boy's home, because the judge handling the case was working there Tuesday.

At the family's home, a wreath with purple and gold flowers hung at the end of a long gravel driveway leading to the house. A young man who came out of the home said the family wasn't ready to talk about what happened. He said he was related to the siblings and then walked back into the home without giving his name.

Grief counselors were on hand Tuesday at Ozark High School, where the sister was a sophomore basketball player and the boy is in ninth grade, Superintendent Jim Ford said. Ford declined to talk about the siblings' relationship or whether they had problems at the school, saying the family asked him not to discuss it.

"Our kids are hurting and this poor family is suffering," Ford said. "It's been a pretty tough day."

He wouldn't talk about how long the siblings had been enrolled at the school, but said the halls were quiet when students trickled back in after the long holiday weekend. The school's basketball games Tuesday against Shiloh Christian were canceled.

Inside the high school, another bouquet of purple and gold flowers — the school's colors — sat atop a receptionist's desk along with a ribbon bearing the sister's uniform number. The Associated Press is withholding the girl's name to not identify her brother, since he has not been formally charged.

"Praying For The Lady Hillbillies" and the siblings' family, a note near the flowers read, referring to the school's mascot. It was signed, "With Our Deepest Sympathy, The Shiloh Lady Saints," the team that the girls' basketball squad had been scheduled to play Tuesday.